# Basic Glossary (Naval architecture terms)

## Basic Glossary (Naval architecture terms)

__Basic Glossary__After perpendicular: AP, the point where the aftermost section crosses the design water line (DWL). On commercial vessels, generally located on the vertical rudder post.

Beam: The maximum breadth of the hull.

Bow: The forward end of the ship.

Bulbous bow: A prominent appendage attached to the bow in order to reduce resistance and thus reduce required horsepower.

Buoyancy force: A ship displaces a certain amount of water and the pressure of the water on the external surface of the underwater body causes this upward force.

Buttock lines: Regularly spaced reference planes cutting the ship's hull parallel to the centerline, generally spaced one,two or four feet apart.

Coefficients of form: Geometric qualities used to describe the ship more precisely. Presented as ratios or dimensionless coefficients. The most common being the block coefficient, Cb, which is equal to the displacement divided by the length times beam times draft.

Depth: The vertical distance from the baseline, or keel, to the top of the freeboard deck, measured at mid-length of the vessel.

Displacement: The weight of the water displaced by the vessel. Salt water equals 64 pounds per cubic foot.

Draft: The depth of the vessel below the waterline measured vertically to the lowest part of the hull or other reference point. Forward, aft, and mean draft are commonly found.

Forward perpendicular: FP, the point where the design waterline crosses the forward most section of the hull.

Gravity force: Downward force equal to the sum of all the weights on the ship. Acts at the center of gravity, point G on the diagram.

Gross tonnage: A measure of the capacity of the ship in which 1 ton is equivalent to 100 cubic feet.

Heel: The inclination of the vessel to one side vice roll, which is the angular motion in waves.

Keel: The principal fore and aft component of a ship's framing, located along the centerline of the bottom.

Length Between Perpendiculars: The length between the forward and aft perpendiculars.

Length OverAll: The extreme length of a ship measured from the foremost point to the aftermost point.

Long ton: Equal to 2,240 pounds.

Metacenter: The point where the intersection of a vertical line drawn through the center of buoyancy of a slightly listed vessel intersects with the centerline plane.

Metacentric height: The distance between the center of gravity and the metacenter.

Planimeter: A tool used to measure the distance around a section in order to develop accurate lines drawings.

Port: The left hand side of the ship.

Resistance: A force that opposes the forward motion of a ship through the water. Broken down into frictional and residual, where residual includes air and eddy-making resistance, but is primarily wave-making resistance.

Section: The intersections with the hull of transverse planes perpendicular to the centerline plane of the ship.

Stability: The tendency of a ship to remain upright or the ability to return to normal upright position when heeled by the action of waves, wind, etc.

Starboard: The right hand side of the ship.

Stern: After end of the ship.

Superstructure and deckhouse: The structures built above the hull form, ie. pilothouse and accomodation areas.

Table of Offsets: Table of coordinates of a ship's form, ie. height above the baseline and half-breadths at each section.

Waterlines: The line of the water's edge when the ship is afloat.

Weights and splines: Small weights and plastic pieces used to draw "fair" lines for ship's lines drawings.

**Nyein Zaw Tun**- Admin
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Location : Singapore

Job/hobbies : Naval Architect

Registration date : 2008-09-05

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